Use of solid, transition metal-based, olefin polymerization catalyst components is well known in the art including such solid components supported on a metal oxide, halide or other salt such as widely-described magnesium-containing, titanium halide-based catalyst components. Such catalyst components are commonly referred to as “supported”. Although many polymerization and copolymerization processes and catalyst systems have been described for polymerizing or copolymerizing alpha-olefins, it is advantageous to tailor a process and catalyst system to obtain a specific set of properties of a resulting polymer or copolymer product. For example, in certain applications, a combination of acceptably high activity, good morphology, desired particle size distribution, acceptable bulk density, and the like are required together with polymer characteristics such as stereospecificity, molecular weight distribution, and the like.
Typically, supported catalyst components useful for polymerizing propylene and higher alpha-olefins, as well as for polymerizing propylene and higher olefins with minor amounts of ethylene and other alpha-olefins contain an internal electron donor component. Such internal electron donor is an integral part of the solid supported catalyst component and is distinguished from an external electron donor component, which together with an aluminum alkyl component, typically comprises the catalyst system. While the internal electron donor is an integral part of the solid supported component, the external electron donor may be combined with the solid supported component shortly before the combination is contacted with an olefin monomer or in the presence of olefin monomer. The external electron donor is commonly referred to as a selectivity control agent (or “SCA”), and the supported catalyst component is commonly referred to as a procatalyst.
Selection of the internal electron donor can affect catalyst performance and the resulting polymer formed from a catalyst system. Generally, organic electron donors have been described as useful in preparation of the stereospecific supported catalyst components including organic compounds containing oxygen, nitrogen, sulfur, and/or phosphorus. Such compounds include organic acids, organic acid anhydrides, organic acid esters, alcohols, ethers, aldehydes, ketones, amines, amine oxides, amides, thiols, various phosphorus acid esters and amides, and the like. Mixtures of organic electron donors have been described as useful when incorporated into supported catalyst components. Examples of organic electron donors include dicarboxy esters such as alkyl phthalate and succinate esters.
In current practice, alkyl phthalate esters are commonly used as internal electron donors in commercial propylene polymerization catalyst systems. However, certain environmental questions have been raised concerning continued use of phthalate derivatives in applications where human contact is anticipated.
Particular uses of propylene polymers depend upon the physical properties of the polymer, such as molecular weight, viscosity, stiffness, flexural modulus, and polydispersity index (molecular weight distribution (Mw/Mn)). In addition, polymer or copolymer morphology often is critical and typically depends upon catalyst morphology. Good polymer morphology generally involves uniformity of particle size and shape, resistance to attrition and an acceptably high bulk density. Minimization of very small particles (fines) typically is important especially in gas-phase polymerizations or copolymerizations in order to avoid transfer or recycle line pluggage.
The art presently recognizes a finite set of compounds suitable for use as internal electron donors in supported catalyst components. With the continued diversification and sophistication of applications for olefin-based polymers, the art recognizes the need for olefin-based polymers with improved and varied properties. Desirable would be internal electron donors in supported catalyst components that contribute to strong catalyst activity and high hydrogen response during polymerization. Further desired are internal electron donors in supported catalyst components that produce propylene-based polymers with high isotacticity, commonly expressed as a xylenes soluble fraction (XS) and/or final melting temperature (TMF).
The invention described relates to use of an internal modifier (internal electron donor) in a propylene polymerization catalyst component, which contains at least two carbonate functionalities.
Accordingly, one embodiment of the invention is a solid, hydrocarbon-insoluble, catalyst component useful in polymerizing olefins, said catalyst component containing magnesium, titanium, and halogen, and further containing an internal electron donor comprising a compound having a structure:[R1—O—C(O)—O—]xR2 wherein R1 is independently at each occurrence, an aliphatic or aromatic hydrocarbon, or substituted hydrocarbon group containing from 1 to 20 carbon atoms; x is 2-4; and R2 is an aliphatic or aromatic hydrocarbon, or substituted hydrocarbon group containing from 1 to 20 carbon atoms, provided that there are 2 atoms in the shortest chain connecting a first R1—O—C(O)—O— group and a second R1—O—C(O)—O— group.